1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine, or more in particular to an ignition apparatus of electronic distribution type for a multi-cylinder internal combustion engine.
2. Description of the Prior Art
A conventional ignition apparatus for an internal combustion engine is disclosed in JP-A-60-209667, in which a negative feedback circuit including current-detecting means is used to control the current in a switching device for controlling the interruption of the primary current of an ignition coil. In applying this type of ignition apparatus to a multi-cylinder internal combustion engine, it is recommended that a part of the apparatus be used in common in order to avoid multiplication of equipment and the resulting increased cost. Specifically, a conventional ignition apparatus for a double-cylinder internal combustion engine uses a current-detecting resistor and a feedback circuit, or the like for controlling the current of a pair of switching transistors.
Further, JP-A-60-209668 discloses an ignition apparatus for an internal combustion engine having four or eight cylinders, comprising four power transistors for controlling the primary current of the ignition coil, in which the four power transistors are provided with a common current detection circuit and a common feedback circuit.
In the above-mentioned prior art apparatus, however, the fact that a single current detection resistor and a single feedback circuit are shared among all switching devices makes it impossible to control all the switching devices if a given switching device is damaged due to a shorting or the like, thereby stopping the ignition of all the cylinders, thus stopping the engine.